The dual or two mode method of analyzing materials for fluorescent properties by subjecting the materials to monochromatic and polychromatic excitation is a known method. It is described in "The Two-Mode Method for Measurement in Formulation with Fluorescent Colorants", by F. T. Simon, Journal of Color and Appearance, Vol. 1, No. 4, February/March 1972, pages 5-11. In accordance with this method, the test sample is alternately illuminated with monochromatic and polychromatic energy. The monochromatic energy is varied over a wide band and the reflectance of the material is determined across such band. Then, the sample is illuminated with polychromatic light and the light reflectance of the sample is again determined across the same bandwidth and the two results are compared to determine the degree of fluorescence.
In accordance with prior art techniques, spectrophotometers are available which operate both a monochromatic mode and a polychromatic mode. To perform the two mode technique, the measurements are first taken in the monochromatic mode, the spectrophotometer is then switched to the polychromatic mode and the further measurements are taken. Resultant data can then be analyzed either manually or by use of a computer.
One application where such a technique is particularly advantageous involves mixing paints or dyes to produce a resultant combination that matches a desired color. In attempting to predict a precise formula for producing the desired color, it has been customary to use the Kubelka-Munk formulas which are useful only in connection with the true spectralreflectance data without any distortions due to fluorenscence. The two mode technique provides such true spectral reflectance data.